The long-term objective ofthis project is to contribute to our understanding ofthe mechanisms of visual representation by cortical networks. Neuronal gain, measured as the continuous slope ofthe relationship between stimulus input and cellular outpiut, is a measure of neuronal sensitivity to the stimulus and a defining element ofthe contribution of single neurons to network operations. Previous work has identified a role for network-driven synaptic activity in modulating the input-output gain of cortical neurons. In addition, synchroiQ'between local network mputs may determine the magnitude ofthe impact of network activity on neuronal gain. Previous studies have also suggested that gain modulation and population synchrony play roles in mediating visual perception. However, even at the earliest stages of cortical visual processing, die relationship between individual neurons and the surrounding local network is poorly understood. The main goals ofthe work proposed here are therefore 1) to determine the relationship betweoi cellular mechanisms of contrast gain control and networic synchrony and 2) to examine tiie interacti(H) between population synchrony and visual perception. To tiiat end, the first Aim focused on many simultaneous recordings of cortical neurons during presentation of stimuli with varying prqierties. The second Aim will use a behavioral task in which awake bdiaving animals discriminate between visual stimuli of vaiying contrast In one series of expraiments, tiiis task will be combined witii population recordings of neimms that make up local netwoiks in primary visual cortex. The results of these eiqieriments are expected to provide novel insights into the relation^p between tiie temporal dynamics of population activity and cellular mechanisms of gain control. In addition, they will graierate a better understanding of tiie role of synchronous cortical networic activity in visual perception.